Our objective is to elucidate the hereditary control of organelle structure and function by studying Mendelian (nuclear) and non-Mendelian (organelle) mutations affecting chloroplasts and mitochondria. We are especially interested in defining the roles played by the chloroplast and mitochondrial genomes in the biogenesis of these organelles and in mapping these organelle genomes by a combination of genetic and physical methods. The unicellular green alga Chlamydomonas reinhardtii is a model system which allows isolation and characterization of non photosynthetic mutants lacking many different chloroplast components (acetate requirers) and mutants with certain altered mitochondrial structures or functions (obligate photoautotrophs). In addition, antibiotic resistant mutations affecting organelle ribosomes and electron transport in the chloroplast or the mitochondria can be readily obtained. In no other eukaryotic cell at present can mutations of both the chloroplast and mitochondrion be investigated to determine the genetic interrelationship of these organelles to the nucleus and to each other. We are also attempting to define the formal genetic rules by which chloroplast and mitochondrial genes are inherited and to explore the mechanisms responsible for their segregation and recombination.